This invention relates to the control of the actuator arm and suspension arm of a magnetic data storage disk drive and, more specifically, to the control of the actuator suspension arms in a manner to cancel or eliminate inertia effects of the magnetic read/write transducer and actuator assembly on the actuator arm and actuator mechanism.
Magnetic data storage disk drives typically have multiple magnetic recording disks, which are non-magnetic disk-shaped substrates with a stable magnetically coercively-alterable coating layered on the surface of the substrate. A plurality of such magnetic recording disks are assembled in stacks. The disk surface coating receives and records individual data bits in a magnetic domain for each bit signal sent to the magnetic read/write head flying above the revolving disk.
Over the past several years with the materials used, the techniques for coating the surfaces of the disks and control of the magnetization of the surface domains have improved to the point that, in orders of magnitude, data domains on an area of a modern magnetic data storage disk may be smaller and more densely positioned, permitting vast increases in the storage capacity of such disk drives or, alternatively, permitting a very significant reduction in size of the disk pack or disk stack and the disk drive. With the improved storage capability now available, significant performance improvement of the disk drives and storage capacity has evolved.
One of the benefits of the improved storage capacity is the reduction in size of the disk drives. Smaller disk drives allow faster rotation of the disks with limited power. Faster rotation permits quicker xe2x80x9cseekxe2x80x9d times in accessing a particular selected data location on the magnetic disk.
In order to fully utilize the storage capability of the magnetic disks, the placement of the magnetic read/write head must be refined to further record data and read data in still denser patterns.
One problem associated with the higher data density on the magnetic data storage disks is the requirement for higher resolution in placement of the magnetic read/write head over a selected data track of the disk. Placement of the magnetic read/write head typically is accomplished by an actuator and actuator arm. A typical actuator is a voice coil motor having the capability of moving one component of the voice coil motor relative to another fixed member in a precise manner. The actuator displaces the actuator arm relative to the actuator frame around a pivot axis. An actuator is typically formed to have an arm extending in proximity to a recordable surface of the magnetic storage disk. Where both surfaces of such a disk are recordable, there is an actuator arm for each side of the magnetic storage data disk. The actuator arm supports a further extension on the distal end of the actuator arm. The extension serves as a suspension or suspension arm for a magnetic read/write head and provides stable support for the magnetic read/write head.
In recording disk drives due to the limited resolution of the actuator drive, the actuator is capable of only limited positioning of the suspension and the read/write head.
To significantly increase the resolution of the actuator and the number of recording tracks on a data storage disk and therefore increase the data capacity of the disk, the suspensions have been provided with electronically actuated micro-actuators. Micro-actuators are designed in a number of different ways, such as by using magneto-strictive devices, piezo-electric members, bimorphic materials or other materials or structures that change at least one dimension of the element in response to connecting therewith or impressing thereon an electronic signal of a selected polarity. The micro-actuator will respond in an opposite manner to an electronic signal of an opposite polarity.
Many examples of micro-actuator construction are known and any of them may be inserted into one leg of a suspension arm or implemented into the suspension such that its dimensional change effects a movement of the magnetic read/write head to one side or the other of the xe2x80x9cnullxe2x80x9d or no electronic signal position. Typically, the read/write head may be displaced to positions on either side of the null position.
Examples of micro-actuators incorporated into an actuator arm assembly are U.S. Pat. No. 4,858,040 as issued to Henry Hazebrouck, which uses bimorphic materials, and U.S. Pat. No. 6,052,251 as issued to Khogrow Mohagerani, which uses a piezo element.
The direction of movement of both the suspension arm and the magnetic read/write head is controlled by the polarity of the electronic signal transmitted to the micro-actuator. For example, a piezo-electric element will bend whenever an electrical voltage is applied thereto, and a reversal of the polarity of the voltage will cause the curvature to be in the opposite direction. Similarly, whenever a magneto-strictive device is employed, the length of the device changes in proportion to the voltage applied thereto. Reversal of the polarity of the electrical signal will cause the device to change dimension in the opposite direction, either contracting or extending depending upon the polarity of the magneto-strictive device.
By placing such an element of selected size in one of two legs of an actuator suspension and sending either positive or negative electronic signals to the element, the expansion or contraction of this element distorts the relatively weak suspension and displaces the magnetic read/write head laterally with respect to the actuator arm, as described above.
One by-product of the size reduction afforded by the higher density of recording on the disk or disks of the disk drive is that as actuator assembly members are reduced in size the cross-sectional area of various portions of components, such as the actuator arm and suspension, are reduced exponentially. Accordingly, the inherent stiffness of the component is reduced or compromised as the cross-sections are reduced.
With reduced or compromised stiffness, the inertia of the components of the actuator assembly becomes a more critical factor and degrades the seek time of the disk drive, thereby adversely affecting the efficiency of the disk drive in both recording and retrieving of the data.
Inertia within the actuator assembly will cause undesired displacement of the actuator arms about the actuator pivot axis, further compromising the accuracy of the placement of the magnetic read/write head until the inertia forces are dissipated and the actuator arm returns to the selected position as controlled by the voice coil motor. This dissipation of forces and the return of the actuator arm to its selected position is referred to as xe2x80x9csettle out,xe2x80x9d and the delay in being able to electronically access the magnetic read/write head caused by the settle out time degrades the seek time of the disk drive. xe2x80x9cSeekxe2x80x9d time is the sum of the periods of time from the receipt of the commands to reposition the magnetic read/write head over a selected track until the actuator has attained the new position, plus the time (if a serial function) to displace the magnetic read/write head relative to the actuator arm and settle out time and, lastly, the time until the designated location on the recording track passes under the magnetic read/write head. The component of seek time that may be affected most efficiently is the settle out time of the actuator arm. If settle out time of the actuator arm may be influenced or significantly reduced, this permits more seek operations within a set time period and, consequently, improves the through-put of the disk drive in either writing or reading the disks.
Whenever a coarse or null position of the actuator is selected, the voice coil motor of the actuator drive quickly repositions the actuator arms to predefined positions corresponding to the null position for the group of tracks within which the desired data or recording location is found. The voice coil motor acts to resist the inertia of the actuator arms. However, the inertia of the further repositioning of the magnetic read/write head on the distal ends of the suspension arms in selecting the precise recording track position causes an undesired force acting on the actuator arms causing a momentary deviation from the null position selected, which could require additional settle time before the data under the magnetic read/write head may be written to the disk surface or the data read from the disk surface.
With the reduction in size of the disk drives, the selecting and driving of micro-actuators on the actuator arms suspension to select the track requires an extensive wiring harness or a great number of conductors in a flexible cable. This additional mass extending to the distal end of each suspension also increases the inertia of the suspension supporting each magnetic read/write head as the conductor must extend past the end of the actuator arm to the suspension.
If the data is written to the disk during the period that the head is inertially displaced laterally from the design recording path, the recorded data will not be readable by a magnetic read/write head positioned properly over the design path position for the particular data track. Similarly, for properly positioned recorded data, the data will not be reliably readable due to the inertial deviation of the magnetic read/write head from the design recording track position due to the mass of the total suspensions shifting the actuator arms. Accordingly, the settle time must be allowed to permit the suspensions to stop oscillating and stabilize their positions as well as permitting additional settle time for the actuator.
With 50,000 data tracks per inch (tpi) or 1970 tracks per millimeter (tpmm) the distance from the centerline of each of the concentric recording tracks to the centerline of an adjacent recording track is about 0.00002 inches (0.50 microns). A very small amount of oscillation of a magnetic read/write head supported on the end of the suspension and the actuator arm can easily, albeit momentarily, deflect the position of the actuator arm comb and require a longer seek time to insure the reliable reading or writing of data to the magnetic disk. The extended seek times over a period of time can cumulatively reduce the data throughput of the magnetic read/write head and thus reduce the efficiency of the disk drive.
If the affects of the inertia forces encountered by the actuator arms can be controlled or counteracted, the actuator arms will not be as affected by the movement of the suspensions and magnetic heads and the resulting inertia. The magnetic read/write heads will seek and settle in their design positions much more rapidly, therefore permitting shortened access times for positioning the magnetic read/write head over the desired data track for either reading data from or writing data to the selected data track of the magnetic storage disk.
It is an object of the invention to counteract the detrimental effects of inertia caused by the displacement of the magnetic read/write heads and suspension arms of the magnetic disk drive.
It another object of the invention to cancel the inertia of a first magnetic read/write head and suspension moving in a first direction with the inertia of a second magnetic read/write head and suspension moving in a second direction.
It is an additional object of the invention to simultaneously displace a first portion of the magnetic read/write heads and the head suspensions of a disk drive in a first direction and a second portion of the magnetic read/write heads and the head suspensions in a second opposite direction.
It is still another object of the invention to physically select a first group of magnetic read/write heads and physically select a second group of magnetic read/write heads and to control lateral displacement of said first and second groups electronically, thus moving the two groups of magnetic heads in opposite directions to reduce inertia effects in an actuator assembly.
It is still an additional object of the invention to physically select a first group of magnetic read/write heads and physically select a second group of magnetic read/write heads and to control lateral displacement of said first and second groups electronically with a single electronic signal provided to each micro-actuator positioning each magnetic read/write head of both groups.
It is a still further object of the invention to fabricate a first group and a second group of micro-actuators with an electronically controlled element connected in opposite polarity so as to respectively expand or contract in response to a first polarity signal and contract or expand in response to a second polarity signal.
These and other objects of the invention are accomplished and the deficiencies of the prior art are overcome by the invention summarized below in the Summary of the Invention.
This Summary of the Invention is provided as a brief understanding of the invention and is not intended to be limiting of the invention in any manner.
In summary, a conventional actuator assembly may be modified to form the invention. The modification is accomplished in the wiring of the micro-actuator on each actuator arm. The micro-actuator, without regard to the type of element used, has a polarity associated with its physical formation. A micro-actuator may be one of a variety of devices from which movement or displacement of attached members may be derived whenever energized with an electrical signal. For example, magneto-strictive, piezoelectric, bimorphic materials or any other type device or material that changes dimensions or shape in response to impressing an electrical voltage across the electro-active element of the micro-actuator may be used to form the micro-actuator.
In this invention, the micro-actuators are divided into two groups. For ease of description and discussion, the groups may be designated as an xe2x80x9cAxe2x80x9d group and a xe2x80x9cBxe2x80x9d group.
The A group and the B group should be made up of equal or substantially equal numbers of micro-actuators. As an example, the A group micro-actuators will be attached to the micro-actuator mountings on a read/write head suspension to flex, extend or contract to displace the magnetic head away from a null position responsive to an electronic signal of a first polarity. The group B micro-actuators will be identical in physical type and structure to the A group micro-actuators. Further, the suspensions of the B group are installed in an identical physical orientation relative to each disk recording surface, (i.e., as viewed from a position where the suspension and micro-actuator are viewed with the magnetic disk surface behind the suspension, and the micro-actuator is located in one leg of the suspension or alternatively installed in an opposite physical orientation relative to the disk recording surface and wired in a reversed manner or polarity from the A group micro-actuators). Thus, the micro-actuators of the B group will cause the movement of the magnetic read/write heads in the opposite direction to the movement of the micro-actuators of the A group relative to the axis of rotation of the disk.
Whenever the micro-actuators of the B group are installed in a reversed physical orientation from the micro-actuators of the A group, wiring connections must be reversed to accomplish the opposite direction movement of the suspensions and magnetic heads of one group relative to the other group.
The designation of the group A micro-actuators and the group B micro-actuators may be made in a number of ways. The typical multiple disk drive has a stack of disks and an actuator member which comprises a journal defining the pivot axis and a plurality of arms extending from the actuator member journal. Each arm extends between two adjacent disks or above or below the top or bottom disk respectively. Each actuator arm inserted between the adjacent disks supports two suspensions having two micro-actuators and two magnetic read/write heads, one on each suspension. The head positioning assembly, including voice coil motor armature, journal and actuator is commonly referred to as an actuator.
Thus, if all the suspensions and micro-actuators are identically manufactured and assembled and are only reversed whenever the suspensions are attached to the actuator arm so that the magnetic read/write head faces an associated magnetic disk recording surface and if the same signal is applied to all of the micro-actuators, the Group A micro-actuators may be the odd numbered micro-actuators and the group B micro-actuators may be the even numbered micro-actuators where the micro-actuators are numbered sequentially from one end of the actuator arm and suspension stack to the other end thereof.
With regard to the immediately above described arrangement, for example, the A group micro-actuators will move the magnetic read/write head outward from and away from the disk stack rotational axis and the B group micro-actuators will move the magnetic read/write head inward and toward the disk stack rotational axis in response to each of the micro-actuators receiving an identical command signal of a first polarity. If the signal polarity is reversed, the micro-actuators of the A and B groups will move in directions opposite to those described above.
Whenever the term xe2x80x9crecording positionxe2x80x9d is used, the term is intended to include the position occupied by the magnetic read/write head during either a read cycle or operation or a write cycle or operation.
By way of further example, if the upper most one-half of the micro-actuators are desired to be moved in one direction (e.g., inwardly toward the disk axis) and the lower one-half of the micro-actuators are desired to be moved in the opposite direction (e.g. outwardly from the disk axis) in response to a single signal of predetermined polarity, some of the micro-actuators of the system either would have to have the polarity of the micro-actuator reversed or the wiring connections reversed in polarity. As in this example, the odd numbered micro-actuators in the upper half of the micro-actuators would require a reversed polarity wiring or the micro-actuator installed in a reversed position relative to the suspension and the even numbered micro-actuators in the lower half treated in the same manner.
On the other hand, the polarity of the wiring connections for both micro-actuators supported on the actuator arms disposed between adjacent disks and the topmost and bottommost micro-actuators must be opposite to each other in order to get the heads disposed on a single actuator arm to move in the same direction. In this design scenario, the polarity of the connections on a selected actuator arm would be reversed relative to the respective connections of the next adjacent arm.
Various other arrangements may be brought to mind of the person of ordinary skill in the art after understanding this invention.
Half or substantially half of the micro-actuators must be displaced in a direction opposite to the other half. The essential aspect of the invention is to cause inertia of one half of the head movement to counteract or cancel the inertia from the other half of the head movements.
In order to reduce the wiring needed to select the appropriate track, the micro-actuators control wiring is simplified by connecting all micro-actuators through a single trunk conductor and a plurality of branch conductors to a single signal causing all micro-actuators to be energized by the same signal.
By using a single signal to command the micro-actuators movement, the wiring of the micro-actuators is greatly diminished and simplified, resulting in other benefits.
This Summary of the Invention is intended as a brief summary description of some of the various embodiments including the preferred embodiment of the invention and is not intended to limit the invention in any manner.
A more complete and detailed understanding of the invention may be had from the attached drawings and the Detailed Description of the Invention which follows.